At SCRIW this year, we had a fairly steady stream of requests for Gangnam Style, which we eventually obliged before alliance selection and during The Great Quarterfinal Breakdown.
If only we had this–we could’ve worn out every hyperactive freshman in the building!
http://labs.echonest.com/Uploader/index.html?trid=TRLMYSS139E7C79031
The stuff going on to make that possible is pretty neat too:
The app works by sending your uploaded track over to The Echo Nest, where it is decomposed into individual beats. Each beat is then analyzed and matched to other similar sounding beats in the song. This information is used to create a detailed song graph of paths though similar sounding beats. As the song is played, when the next beat has similar sounding beats there’s a chance that we will branch to a completely different part of the song. Since the branching is to a very similar sounding beat in the song, you (in theory) won’t notice the jump. This process of branching to similar sounding beats can continue forever, giving you an infinitely long version of the song.
Or, if you’re in a game hint mood… 
Enjoy.